1. Technical Field of the Invention
The present invention relates to an apparatus for automatically detecting the completion of a cutting operation of a cutting machine, to stop the rotation of a spindle driving motor thereof.
2. Description of the Related Art
Cutting machines such as a thread cutting machine having an automatic tool retracting device which detects the completion of the cutting to automatically return or retract a cutting tool to an inoperative position are known.
The assignee of the present application has proposed prior Japanese applications directed to die heads having an automatic tool retracting device, as mentioned above (e.g., Japanese Unexamined Utility Model Publication No. 59-100527, Japanese Unexamined Patent Publication Nos. 56-146620 and 57-15628).
The tool retracting device usually includes a tool retracting lever having a front end which lies in the center of a center opening of a die head so as to come into contact with a leading end of a pipe to be cut, which is axially extended in the die head when the pipe comes to a predetermined cutting completion position, so that the tool retracting lever can be moved by the pipe when the pipe is brought into the contact with the tool retracting lever and automatically and rapidly retract or return the tool (or tools) to its (or their) initial position (inoperative position) by means of a scroll mechanism provided in the die head.
With the tool retracting device, it is not necessary for an operator to continuously stand by the machine to observe the ending of the cutting operation. In addition, the tool retracting device contributes to the formation of a good appearance of the cut surface of the pipe.
In the prior art as mentioned above, however, the tool retracting operation is achieved by returning the tool(s) to the initial inoperative position. Namely, the concept of automatically stopping the spindle driving motor in accordance with the stoppage of the completion of the tool retraction is not suggested by this prior art. In other words, although the tool(s) are automatically retracted by the automatic tool retracting device, the motor continues to rotate until the operator turns the motor OFF. This is disadvantageous from the view points of a safe operation and a lowering of electrical power consumption.